Impact device using a gas as its medium

ABSTRACT

An impact device using a gas as its medium is formed of an air pump and an impact cylinder. The air pump and the impact cylinder are respectively divided by a pump piston and a hammer piston into upper and lower chambers which intercommunicate upper with upper and lower with lower through valves which regulate the flow of high and negative pressure gas causing the downward impact stroke of the hammer piston onto the tool at the lower end of the impact cylinder and the downward stroke of the pump piston to begin simultaneously after the pump piston has reached its top dead point compressing the air in the upper chamber to the maximum and generating the maximum negative pressure in the lower chamber. There are further provided means for communicating the upper and lower chambers of the pump cylinder when the pump piston has reached the lower dead point and means for communicating the upper chamber of the impact cylinder with the means for connecting the lower chambers of the two cylinders.

United States Patent [151 Matsuo [45] July 2, 1974 IMPACT DEVICE USING A GAS AS I'IS MEDIUM [76] Inventor: Susumu Matsuo, Minamiitsuski 196,

Chosen-cho, Sunto-gun, Shizuoka-ken, Japan 22 Filed: Sept. 6, 1972 21 App1.No.:286,730

[30 Foreign Application Priority Data Sept. 23, 1971 Japan 46-73805 [52] US. Cl 173/116, 60/542, 60/547, 60/571, 60/591, 60/593 [51] Int. Cl B25d 9/08 [58] Field of Search........ 173/116, 14; 60/542, 547, 60/571,591, 593

[56] References Cited UNITED STATES PATENTS 819,011 4/1906 Gibson .j. 173/116 X 942,163 12/1909 Berner 173/116 X 1,071,387 8/1913 Behr 173/116 n me y. Exam n r-J me. Raiser. Attorney, Agent, or FirmKurt Kelman [57] ABSTRACT An impact device using a gas as its medium is formed of an air pump and an impact cylinder. The air pump and the impact cylinder are respectively divided by a pump piston and a hammer piston into upper and lower chambers which intercommunicate upper with upper and lower with lower through valves which regulate the flow of high and negative pressure gas causing the downward impact stroke of the hammer piston onto the tool at the lower end of the impact cylinder and the .downward'stroke of the pump piston to begin simultaneously after the pump piston has reached its top dead point compressing the air in the upper chamher to the maximum and generating the maximum negative pressure in the lower chamber. There are fur ther provided means for communicating the upper and lower chambers of the pump cylinder when the pump piston has reached the lower dead point and means for communicating the upper chamber of the impact cylinder with the means for connecting the lower chambers of the two cylinders.

1 Claim, 6 Drawing Figures PATHITEHJML 2 [W4 SHEET 5 BF 5 Fig.6

BACKGROUND OF THE INVENTION Crushing operations requiring extremely great crushing power, such asthe crushing of raw limestones, preliminary breaking of quarried stones for gravel before feeding to a crusher, crushing of concrete roads and buildings and crushing of clinker in blast furnaces, have conventionally been carried out by mounting a compressed-air-operated pneumatic breaker on the end of the arm of an operation truck like power shovel or backhoe, connecting the pneumatic breaker to another truck carrying a large (100 ZOOHP) air compressor with a long, large hose that can be wound and driving the breaker by the use of the expanding force of the compressed air prepared by the air compressor truck. While the breaker is driven by the air the operation truck is moved from place to place according to necessity and the air compressor truck is kept at a fixed position. As is well known, however, this pneumatic breaker which releases the used air into the atmosphere during each rotation is very low in mechanical efficiency owing to the mechanical loss of the air compressor, the mechanical loss of the impact device of the breaker, the heat loss at both the compressor and the impact device andthe friction at the inside of the hose.

Furthermore, the hose is constantly being dragged over the ground and is sometimes even pulled tense by the movement of the operation truck. Also the hose is run over by the heavy dump car carrying the stones for crushing. Because of fast wear and troublesome handling the hose becomes one of the weak points of the operation.

These disadvantages are unavoidable because no impact device capable of exhibiting powerful operating effect by utilizing a power source mounted on the operation'truck itself has yet been developed. Impact devices so far developed and now under development invariably require an unnecessarily large cycle for the hammer pistonimpulse so that the impact speed of the hammer piston can be increased to generate large impact force. Therefore, it is necessary for such impact device to cancel the extremely great moment of inertia generated at each end of the stroke of the unnecessarily heavy hammer piston and to waste power than might be expected in reversing the direction of the stroke. The greater part of the imput energy is thus wasted as the mechanical loss of the equipment.

In other words, only a half of each cycle counts toward impact stroke speed of the hammer piston. So

in order to obtain high piston speed it is necessary to increase the number of cycles per minute toobtain a higher speed. In conventional devices, however, a faster cycle time, results in more power being wasted for canceling the moment of inertia as explained above.

For this reason it is necessary for obtaining an impact device having high efficiency that the hammer piston used be as heavy as possible, that the cycle time be as long as possible, and that the hammer piston travel within practical limits, very irregularly. That is to say, the speed of the downward impact stroke of the hammer piston should be as high as possible, while its upward return stroke after the inertia has attenuated should be sufficiently slow.

. I 2 SUMMARY OF THE INVENTION: Based on this idea, the present invention provides an impact device characterized by selecting the number of hammer piston cycles per minute according to the nature and purpose of the operation, sealing the positive and negative pressures in the air pump by closing the respective valves until the air pump finishes compressing the operatingair so that the heavy hammer piston is held in the starting position at the upper dead point until its impact stroke is started, opening the pair of valves much as an air rifle is triggered as soon as the compression has reached its limit, giving a powerful assistance to the downward impact stroke of the hammer piston by injecting high pressure air into the upper chamber of the hammer piston and applying negative pressure to the lower chamber, properly adjusting the time required for the upward retum stroke of the hammer piston to a half of the cycle time of the air pump, while that for the downward impact stroke is only a small fraction of the cycle time of the driving pump, mounting both the driving pump and the impact device on the operation truck so that the driving pump can ob tain sufficient driving power from the engine ordinarily used to power operate the truck when it is driven and carrying out the crushing operation without having to drag the hose on the ground.

Other advantages and features of the present invention will be morefully understood from the following description of its embodiment when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS EXPLANATION OF THE PREFERRED EMBODIMENT In FIG. 1, A is an air pump whose cylinder 1 contains 7 piston 2 which divides its interior into upper chamber la and a lower chamber 1b. When one of the chambers increases in volume by the motion of the piston 2, the other decreases in volume. Below cylinder 1 and connected thereto is cylinder 3 of the piston-cylinder type hydraulic actuator B which causes piston 2 of air pump A to make regular reciprocal strokes. Piston 4 within cylinder 3 is connected to piston 2 of air pump A by rod 5. The inside of cylinder 3 is likewise partitioned by piston 4 into upper chamber 3a and lower chamber 3b, one increasing its volume when the other decreases its volume. Shaft 6a and 6b are pivotally mounted through the wall of cylinder 3 at its top and bottom and the respective inner ends of these shafts are provided with arms 7a and 7b positioned inside the upper and lower chambers 3a and 3b and at their respective outer ends thereof are provided the outer arms 8a and 8b.

Said outer arms 8a and 8b change over the operation of spool 9 of the spool type change-over valve C attached to the outside of cylinder 3 in the following way. Change-over valve C has one port P for introducing the input liquid pressure from a hydraulic (e.g. oil hydraulic) pump and two ports T, and T for returning it to the tank. According to this embodiment, when spool 9 is at its lifted position the input liquid pressure coming through port P is introduced into lower chamber 3b of cylinder 3 after passing through the valve and lifts piston 4, with the result that the liquid pressure inside upper chamber 3a of the cylinder returns to the tank through port T after passing through the valve. When spool 9 is at its lowered position as shown in the drawings the input liquid pressure is introduced into upper chamber 30 of the cylinder and lowers piston 4, the liquid inside the lower chamber being driven into the tank through port T Therefore, when piston 4 is lifted to push up arm 70 in the upper chamber 3a outer arm 8a pushes down spool 9 to its lowered position, thereby introducing the input liquid pressure into upper chamber 30 and lowering piston 4. Conversely when piston 4 is lowered to push down arm 7b of lower chamber 3b outer arm 8b pushes up spool 9 to its lifted position, thereby introducing the input liquid pressure into lower chamber 3b and lifting the piston 4. As for arms 7a and 7b, when piston 4 acts on one of them and brings spool 9 to the other position by means of the outer arm, the other of them is returned to the ready position by spool The input liquid pressure is produced by a hydraulic pump driven by the power taken from the operation truck.

Thus hydraulic actuator B causes piston 4 to make regular reciprocating impact strokes by means of change-over valve C and drives piston 2 of air pump A through rod 5.

-Air pump cylinder 1 is provided at a lower inside position thereof with axially long opening 10 as shown in the drawings, which brings the parts above and below the piston 2, namely, to the upper chamber 1a and bottom chamber 1b, into communication when piston 2 has reached the bottom dead point. Opening 10 communicates with exhaust valve 12 of cylinder head 1' through passage 11. This opening 10 may be branched into upper and lower parts as shown as 10a and 10b in FIG. 4.

Exhaust valve 12 opens both when strong positive pressure enters passage 11 because of the compression of the air in lower chamber 1b by piston 2 and when piston 2 has reached the top dead point by raising lower end of stem 12' protruding into upper chamber 1a.

Cylinder head 1' is provided not only with exhaust valve 12 but also with intake valve 14 which has opening 13 of the head as its seat. Opening 13 is connected through the intake valve 14 and tube 15 to opening 18 at the top of upper chamber 17a of impact cylinder 17 of the impact section containing hammer piston 16. Intake valve 14 opens both when strong negative pressure is created in upper chamber 1a by the downward stroke of piston 2 as described later and when piston 2 has reached the top dead point in cylinder 1 stem 14 in pushed down by rocker arm 20 operated by the raised tappet.

Impact cylinder 17 is provided at a lower portion on its inside with upper and lower openings 21 and 22 con necting to each other at the branching point below passage 23, one of said openings being opened above the hammer piston into upper chamber 17a and the other being closed by the side of the hammer piston when hammer piston 16 reaches the bottom dead point. The respective vertical positions of said upper and lower openings 21 and 22 are so selected that when hammer piston 16 makes its downward impact stroke upper opening 21 is first closed by the side of the piston and then lower opening 22 is also closed and when the pis-- ton reaches the bottom dead point upper opening 21 is opened into upper chamber 17a but the lower opening 22 remains closed by the piston. As in the case of the aforementioned opening 10 of the air pump cylinder, openings 21 and 22 may be prepared as one long axial opening as far as said relationship is maintained.

Passage 23 which is connected to upper and lower openings 21 and 22 communicates with exhaust valve 12 mounted on the head of the air pump cylinder by means of tube 24 and is further connected to the opening 10 through the passage 11.

Impact cylinder 17 is provided at its lower end with tool 25 for striking the object to be crushed when hammer piston 16 makes its downward impact stroke and reaches the bottom dead point. This tool 25 is returned to its elevated position by a spring 26 or the like in a known way and has its upper end thrust back into the lower chamber of the impact cylinder.

Hammer piston 16 is also provided at its upper end with stopper 27 planted therein. When the hammer piston making its upward return stroke has come to the upper part of cylinder 17, said stopper 27 thrusts into opening 18 at its top and closes the opening 18. The hammer piston continues to rise with the opening 18 at its top closed by stopper 27 until it reaches the top dead point.

In principle air of atmospheric pressure is sealed into the system for the total volume (working volume plus clearance volume) of airpump A and for the volumes of upper and lower chambers 17a and 17b of the impact section. In actual use, however, this air is converted into a gas containing no oxygen similar to the exhaust gas of an internal combustion engine because the oxygen consumed in an explosive reaction with a relatively inflammable gas resulting from the decomposition of the lubricant at the stroke end of the hammer piston in the early stages of the operation. Of course, an inert gas may be sealed into the system instead of air.

The ratio of the cubic capacity of air pump to the total stroke cubic capacity of hammer piston 16 is generally calculated by the total power required. The equipment of the present invention is designed with a large cubic capacity ratio of 1.4 to 1.8 in order to allow hammer piston 16 to make an effective uniform motion with a surplus volume of air always equal to the difference between the two cubic capacities. The most effective ratio of surplus air is selected by the cycle time which is determined by the horsepower of power source and the weight and stroke of the hammer piston, depending on the nature of work. Then, as shown in FIG. 3, the air pump A, hydraulic actuator B and change-over valve C are installed in swing arm 28 of the operation truck, and impact section D is fixed to the end of swing arm 28 by means of articulated connecting rods so that the tool can be faced in the desired direction by moving vertically with the help of position controlling actuator 28'. I

In. order to make this possible, tubes and 24 should be flexible and as short as possible within the limit necessary for allowing the vertical motion of impact section D.

The movement of air and change of pressure in one cycle of this invention will be explained below by referring to FIG. 4a-4f. As piston 2 of air pump A approaches the end of the downward stroke (FIG. 4a), great negative pressure develops in upper chamber la. Then intake valve 14 is opened by this negative pres sure to connect upper chamber 17a of impact section D to said upper chamber 1a through tube 15 and opening 18. On the other hand, the air compressed in lower chamber lb of the pump opens exhaust valve 12 through the opening 10 and the passage 11 and operates as positive pressure in lower chamber 17b of impact section I) after passing through tube 24, passage 23 and openings 21 and 22.

As a result, hammer piston 16 makes an upward re- .turn stroke sucked by the negative pressure from above and pushed up by the positive pressure from below, and then closes the opening 18 with stopper 27 (FIG. 4b).

When stopper 27 closes theopening 18, upper chamber 17a of the impact cylinder forms an enclosed cushion chamber and attenuates the moment of inertia of the rising hammer piston until at last it is-overcome and piston 16 reaches the top dead point. At the same time the piston 2 of the air pump reaches the bottom dead point and thereby the upper chamber 1a of the air pump communicates with the lower chamber lb through opening 10, and the difference between the pressures in the two chambers la and lb ceases to exist to make it impossible for intake and exhaust valve 12 and 14 to remain open. Thus both valves close automatically, and air pump A and impact section D are isolated hermetically from each other. However, considerable amounts of compressed air still remains sealed in the tube 24 and in lower chamber 171; of the impact cylinder, and the inside of the tube 15 is kept under strong negative pressure, so that the hammer piston stays at the top dead point.

Next, the piston of air pump A is forced to make a rising stroke (FIG. 4c).

In this case, since upper chamber 1a of the air pump holds a sufficient volume of air as it communicates with lower chamber 1b through opening 10 as stated above, the air in upper chamber la is compressed and'negative pressure in lowerichamber 1b after piston 2 has gone above opening 10. Intake and exhaust valves 14 and 12 are, of course, not opened by the positive pressure in the upper chamber or by the negative pressure in the lower chamber. Therefore, air pump A and impact section D remain isolated and hammer piston 16 stays at the top dead point due to the positive pressure in the lower chamber of the impact section and the negative pressure in tube 15.

When piston 2 of air pump A presently reaches the top dead point, causing strong positive pressure and strong negative pressure to develop in the upper chamber la and lower chamber lb respectively, intake and exhaust valves 14 and 12 are opened by piston 2 (4d). Lower chamber lb of the air pump then communicates with lowerchamber 17b of the impact section through exhaust valve 12, thereby eliminating the positive pressure obstructing hammer piston 16 from making downward impact stroke and sucking down hammer piston 16. The air highly compressed in upper chamber 1a of the air pump rushes into tube 15 through intake valve 14 and pushes down the hammer piston by acting on its stopper 27.

When piston 16 has lowered and stopper 27 has come out of opening 18 at the top, the high pressure air coming through opening 18 acts on the whole upper side of piston 16, and combined with the sucking action of lower chamber 17b, it makes hammer piston 16 effect a quick downward impact stroke and strike tool 25.

When hammer piston 16 has effected the downward impact stroke and come down below the lower opening 22 (FIG. 44e), lower chamber 17b of the impact section forms a cushion chamber which cushions the hammer piston at the bottom dead point with the help of the counteraction of tool 25. At that time, upper open ing 21 opens for a moment above piston 16 and connects upper chamber 17a of the impact section to the port 23. Therefore, the high pressure gas inside upper chamber flows into passage 23 with a strong moment of inertia owing to the multiplied effect of the violent downward flow communicating with the negative pressure zone inside the passage 23, the difference between the two pressures and the great volume of operating gas in the air pump.

When hammer piston 16 comes above upper opening 21 after being cushioned at the bottom dead point and completes the early stage of the upward return stroke, the inside of upper chamber 17a is kept under suitable negative pressure and the piston of the air pump makes a downward stroke to compress in lower chamber lb the air sucked in from lower chamber 17b of the impact section when intake valve is opened and create nega tive pressure in upper chamber la (FIG. 4 thus causing the hammer piston to proceed with its upward re turn stroke by the pressures of both chambers as described with reference to FIG. 4a.

FIG. 5 is a diagram illustrating the relationship between the cycle time and stroke for the air pump piston and hammer piston of the present invention. Air pump piston 2 shown by solid line opens the exhaust and intake valves 12 and 14 after completing its air compressing action in upper chamber 1a and its negative pres sure generating action in lower chamber lb by rising from bottom dead point BP and reaching top dead point TP. As these valves 12 and 1.4 are opened, hammer piston 16 is sucked into lower chamber 17b by strong negative pressure and makes a downward impact stroke to reach the bottom dead point HP subjected to the injection of the air compressed into upper chamber la by the air pump piston, while the air pump piston makes a downward stroke toward the bottom dead point BP at a given speed. Hammer piston 16 which has reached the bottom dead point HP changes the pressure in the upper chamber of the impact section from positive to negative before the air pump piston reaches bottom dead point BP and then returns to top dead point l-ITP'by the positive: pressure generated in the lower chamber of the air pump. While the air pump piston is making its upward stroke the hammer piston stays at the position HTP.

Thus the pump piston and hammer piston start their respective downward strokes simultaneously. The pump piston makes uniform motion and the hammer piston makes extremely ununiform motion including a stop at the top dead point, though both motions are efv 7 fected regularly. While the pump piston is making its downward stroke the hammer piston completes its momentary downward impact stroke and its upward return stroke.

This can be achieved only by the principle of the present invention characterized by providing intake valve 14 in the passage connecting the respective upper chambers la and 17a of the air pump and impact section and exhaust valve 12 in the passage connecting the respective lower chambers lb and 17b, opening both valves by generating strong negative pressure in upper chamber in and strong positive pressure in lower chamber 1b with the downward stroke of the air pump piston, pushing up the hammer piston to return it to the top dead point when the valves are opened, holding the hammer piston at the top dead point until the air pump piston, which has reached the bottom dead point and closed the valves by eliminating the difference of pressures between the upper and lower chambers, reaches the top dead point and opens the valves, opening the valves at the top dead position to start the downward strokes of both the air pump piston and the hammer piston simultaneously, sucking the air of the lower chamber of the impact cylinder into lowerchamber lb, drawing the air out of the upper chamber of the impact section so that the hammer piston, which has reached the bottom dead point, can readily make the next upward return stroke, compressing the air in the lower chamber by the pump piston in the downward stroke and thereby generating negative pressure in the upper chamber.

in the case of the illustrated embodiment, the exhaust and intake valves 12 and 14 are so designed that they are opened when the pump piston has reaches the top dead point and when the pump piston has madeits downward stroke to generated strong pressures in the upper and lower chambers. However, these valves may also be designed so that they are opened when the pump piston has reached the top dead point, and lead valves or the like may be additionally installed with both valves, said additional valves being opened by the pressures generated in the chambers.

It is also possible to obviate the use of suction valve 14, tappet 19 and rocket arm 20 as shown in FIG. 6 and install, for example, a solenoid-operated valve or bydraulically operated valve 29 incorporating a spring directly above the position of opening 18 into which stopper 27 is thrust, said valve 29 being opened when the pump piston is making a downward stroke, closed when the pump piston reaches the bottom dead point, also closed when the pump piston is making an 'upward stroke and opened again when the pump piston is about to make downward stroke after reaching the top dead point. in this case, the total volume of tube 15 is designed as the clearance volume of air pump A. When the pump piston makes an upward stroke air is compressed also in tube 15, and when it reaches the top dead point valve 29 is opened to have the highly compressed air act on the stopper 27 instantly.

Valve 29 shown in FIG. 6 is usually closed by the spring 29. According to this illustration, spool 9 of change-over valve C is switched over to the lower position so that the pump piston can make a downward stroke after reaching the top dead point and part of the liquid pressure introduced into the upper chamber of the pump piston through passage P is led into the valve through branched passage 30 in order to let the liquid 8. pressure act on piston 29" which is integral with the valve, so that while the pump piston is making a downward stroke the valve is kept open resisting spring 29'. Of course, this valve 29 may be used in place of exhaust valve 12 in such a way that it is kept open by liquid pressure while the pump piston is making a downward stroke and closed by spring 29' while the pump piston is making an upward stroke.

According to this invention, the greater the entire design, the greater area the hammer piston requires because of the ratio between its width and depth. But a large output may be obtained at will by making the hammer piston hollow.

At the each start of operation, the hammer piston 16 is at the bottom dead point and blocks lower opening 22 with its side. So it is impossible to have the positive pressure generated in the lower chamber of air pump A act on the hammer piston from below. For this reason, the negative pressure generated in the upper chamberof air pump is used at the start. This means that it takes time for the hammer piston to start making regular strokes. In actual operation, however, this time may be shortened by providing suction valve 31 at the lower end of lower chamber 17b of the impact section by making a suitable opening there and connecting this valve 31 to passage 23 so that the positive pressure generated in the lower chamber 1b of the air pump can act on the hammer piston from below even if it blocks lower opening 22. Of course, this valve 31 is closed when hammer piston 16 makes a downward impact stroke and compresses the air in lower chamber 1712. Therefore, valve 31 does not interfer with the cushioning of the hammer piston at the bottom dead point.

Air pump A of the illustrated embodiment is shown as operated by hydraulic reciprocating actuator B. But this actuator may be a rotary motor reciprocally driven, for example, by the rod 5 by means of a crank through a link. The power source for operating air pump A may be oil pressure obtained from the hydraulic pump driven by the engine of the operation truck. In this case, while the power is being used for running the truck the hydraulic pump is stopped by disengaging the clutch and when the truck is stopped the pump is operated by engaging the clutch.

What I claim is:

1. An impact device using gas as its medium which comprises in combination,

A. an air pump having an upper and a lower chamher, a movable piston intermediate the upper and lower chamber, an air communication port between the upper and lower chambers, and a piston rod joining the movable piston and projecting through a wall of the lower chamber, said piston rod having disposed thereon a second piston within a hydraulic pump, said hydraulic pump providing drive means for effecting upward and downward strokes of said movable piston at a fixed speed;

B. an impact section consisting of an impact cylinder having an upper and a lower chamber, a hammer piston having a projecting member disposed along an upper surface and means for striking a tool by an opposite surface, a tool projecting from the impact section;

C. an air passage connecting the upper chamber of the air pump with the upper chamber of the impact section, a valve within said air passage and means for receiving in air stopping engagement said projecting member, said valve disposed to prevent exhaust of air from the upper air pump chamber;

D. a second air passage connecting the lower chamber of the air pump with the lower chamber of the impact section, a second valve within said second air passage, said second valve having a stem projecting within the air pump and movable by said movable piston, said second valve disposed for preventing-intake of air into the upper chamber of the air pump; and

E. said combination of chambers and air connecting means effecting start of downward impact stroke of the hammer piston and downward stroke of the pump piston simultaneously by means of pressure F. said air communication port being open when the movable piston is in the bottom dead point; and G. said impact cylinder having means for communieating the upper chamber of the impact chamber with the air passage connecting both of said lower cylinders. 

1. An impact device using gas as its medium which comprises in combination, A. an air pump having an upper and a lower chamber, a movable piston intermediate the upper and lower chamber, an air communication port between the upper and lower chambers, and a piston rod joining the movable piston and projecting throuGh a wall of the lower chamber, said piston rod having disposed thereon a second piston within a hydraulic pump, said hydraulic pump providing drive means for effecting upward and downward strokes of said movable piston at a fixed speed; B. an impact section consisting of an impact cylinder having an upper and a lower chamber, a hammer piston having a projecting member disposed along an upper surface and means for striking a tool by an opposite surface, a tool projecting from the impact section; C. an air passage connecting the upper chamber of the air pump with the upper chamber of the impact section, a valve within said air passage and means for receiving in air stopping engagement said projecting member, said valve disposed to prevent exhaust of air from the upper air pump chamber; D. a second air passage connecting the lower chamber of the air pump with the lower chamber of the impact section, a second valve within said second air passage, said second valve having a stem projecting within the air pump and movable by said movable piston, said second valve disposed for preventing intake of air into the upper chamber of the air pump; and E. said combination of chambers and air connecting means effecting start of downward impact stroke of the hammer piston and downward stroke of the pump piston simultaneously by means of pressure in the upper chamber of the air pump applied to the upper chamber of the impact cylinder and by means of negative pressure of the lower chamber of the impact cylinder when the movable piston has reached a top dead point with maximum negative pressure in the lower chamber; F. said air communication port being open when the movable piston is in the bottom dead point; and G. said impact cylinder having means for communicating the upper chamber of the impact chamber with the air passage connecting both of said lower cylinders. 